I've got a '88 Ford LTL9000 w/ cummins NTC400 in it. We started having overheating issues going over mountains. Long story short we ended up replacing thermostats, water pump, radiator (low flow), and water pump belt. Still overheating, found 2 cracked heads. replaced all 3 head (new from cummins not reman). put old injectors back in. ran fine until we put load behind it and it starts to miss and when you stop at stop sign it wants to cut off like starving for fuel. on interstate you can really hear and feel miss. replaced injectors, no difference. Fuel filter is half full, changed suction line and filter. didn't help. but a different fuel pump on, same thing. put original pump back and started testing. stuck return off gear pump in bucket, no bubbles, service manual tells me that means it's not sucking air. also ran air test on AFC signal line to pump, pass that test, held 20 - 25 psi for 10 seconds or longer. stuck new suction line in bucket and no difference in fuel filter being half full. my next step is to put air test on injectors to see if an oring got rolled or something.... but I'm afraid it's going to pass that test too seeing how it did w/ old injectors and new injectors.. any help would be muchly appreciated, thanks in advance!! ps.. it was not missing before it was torn into to replace heads.